It's been busy couple weeks up in the cloud. First, you had Microsoft release SkyDrive for Mac. Then Google went and released their Google Drive service with a desktop application for the Mac. And now, Amazon has released a desktop application for the Mac for their Cloud Drive service. This application allows users to upload files to the service by simply dragging files or folders to an icon in the menu bar. But on the downside, the application doesn't appear to offer a way to automatically sync your files with the service. You need to manually upload your files after changes are made to them. Nor does it create a dedicated folder on your Mac to manage or view. Amazon does provide 5GB worth of free space though.
So, check it out if you are interested or already a user. It does seem to work well minus a couple shortcomings.